Eddy-current apparatus including a magnetizable metal facing



Jan. 23, 1968 R JAESCHKE 3,365,598

EDDY-CURRENT APPARATUS INCLUDING A MAGbLETIZABLE METAL FACING Filed Aug.31, 1964 2 Sheets-Sheet l FIGI.

3,365,598 EDDY-CURRENT APPARATUS INCLUDING A MAGNETIZABLE METAL FACENGRalph L. .llaeschlre, Kenosha, Win, assignor to Eaton Yale & Towne Ina,a corporation of Ohio Filed Aug. 31, 1964, Ser. No. 393,147 3 (Ilaims.(Cl. 310105) ABSTRAT OF THE DISCLOSURE Eddy-current apparatus comprisingcoaxial relatively rotary polarizing field and ferro-magnetic inductormembers separated by a distance determining a circular magnetic gap. Theinductor at the gap is faced with a magnetic material. This magneticmaterial has wear resistance and corrosion resistance greater than thatof iron. Its electrical resistance is less than that of iron. Thepreferred magnetic material for the layer having these properties isnickel. In general, the nickel or other appropriate material should alsohave an electrical resistance at 20 C. in the range of approximately to8 micro ohm centimeters (with 6.8 preferred). The thickness is in therange of approximately .005 to .030 inch, with .010 inch preferred for amachine having a running gap in the range of approximately & to A2 inch.

Among the several objects of the invention may be noted the provision ofeddy-current apparatus of the class described, the eddy-current inductorof which is improved at the face of its magnetic gap so as to obtainsuperior torque-transmitting functions over a wide range of slip speedsand which will have the subsidiary advantage of beingcorrosion-resistant. Other objects and features will be in part apparentand in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations ofelements, features of construction, and arrangements of parts which willbe exemplified in the constructions hereinafter described, and the scopeof which will be indicated in the following claims.

In the accompanying drawings, in which one of various possibleembodiments of the invention is illustrated,

FIG. 1 is an axial section of an eddy-current coupling embodying theinvention;

FIG. 2 is an enlarged fragmentary cross section taken on line 22 of FIG.1; and

FIG. 3 is a chart illustrating certain torque-slip-speed functionalrelationships.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawmgs.

The invention is an improvement upon apparatus such as shown, forexample, in my United States patent 2,971,- 105.

Various facings have been proposed for the surfaces at the magnetic gapsof electrical machines for providing resistance against corrosion bycoolants employed in their magnetic gaps, or for providing wearresistance in those of such machines which, without the use of eddycurrents, employed magnetic particles in the gaps. The selection offacings to meet these requirements has not resulted in improvements inthe torque vs. slip-speed functions of such machines and in many caseshas resulted in interior functions in that regard. According to thepresent invention, useful primarily in eddy-current machines, aninductor facing on the eddy-current inductor is employed which greatlyimproves the stated functions, while at the same time providingprotection against corrosion.

Referring now more particularly to FIG. 1, there is shown (for purposesof illustration) an eddy-current slip 3,365,538 Patented .ian. 223, i968coupling of known type to which the invention has been applied. Thiscomprises a casing 1 formed by abutted pole rings 3 and 5 which supportan annular field coil 7 and end bells 9 and 11. The end bells 9 and 11respectively contain bearings 13 and 15, surrounding coaxial driven anddriving shafts 17 and 19, respectively. Keyed to the driven shaft 17 isa magnetizable (iron or steel) polar field rotor 21 carryingperipherally disposed and axially extending pole-forming teeth 23. Theends of these teeth or poles face the inner surface of a two-pieceferromagnetic (iron or steel) drum 25 across a running gap 27. Thisrunning gap 27 is made as small as possible consistent with maintainingsafe clearance. A gap of from to /8 inch is typical. The drum 25 isinternally cylindrical. The two sections of the drum 25 are joined by awelded ring 2 (preferably nonmagnetic) in which are suitable radialopenings. The outside cylindrical portions of the drum 25 facecontinuous internal cylindrical surfaces 29 and 31 of the pole rings 3and 5 across small gaps 33 and 35, respectively. The inside portions ofthe drum 25 are, according to the invention, faced as shown at A with amaterial to be particularized below.

When the coil 7 is magnetized by applying current thereto throughsuitable wiring (not shown), a toroidal magnetic flux field passesthrough the members 3, 5, 25, 23 and in doing so crosses the gaps 2'7,33 and 35. The peripheral distribution of flux in the gaps 33 and 35 ishomogeneous so that no coupling torque is transmitted across gaps 33 and35. In the gap 27 the flux is bunched or concentrated at intervals bythe pole-forming teeth 23. Therefore, upon relative rotation of the polemember 21 and the drum 25, the sweeping action of flux-"leldconcentrations will induce eddy currents in the drum 25. Induction ofthese currents is strongest near the inner surface of the drum. The eddycurrents produce a reactive magnetic field with the fields from thepoles 23, to effect a driving slip coupling therebetween.

The drum 25 is supported at one end upon a spider 37 carried uponbearings 39 in the end bell 9. The other end of the drum 25 is supportedupon a disc 41 attached to a flange 43 of the drive shaft 19. Shafts 17and 19 are maintained in alignment by means of a pilot bearing 45.Coolant such as water is introduced through an inlet 4. Part of thecoolant progresses as shown by the lower line of curved darts L throughthe drum 25, then passing along the poles 23. It then escapes throughports 6 into a space 8 from whence it passes to an outlet 10.

Another part of the coolant, as illustrated by the upper line of dartsU, passes around the drum 25 through the magnetic gap 35 to the space 8and then out through said outlet 10. Shaft seals and lubricating meanssuch as shown, or the like, are provided for various bearings butrequire no detailed discussion, being of known type and function. Acontrol generator 12, belt-driven from the shaft 17 as shown, isemployed in connection with the electrical circuit for exciting the coil7. This serves as a speed control by controlling the intensity of thetoroidal field around the coil. Such controls are conventional andfurther description will not be required.

The invention relates to the character of the inner face of the drum 25which defines the outer part of the gap 27 opposite the ends of thepoles 23. In the past, such facings have been variously constructed. Forexample, the sur face was sometimes left bare, thus presenting an ironor steel face, with the result in operation such as shown by the curve Bin FIG. 3. Curve B displays torque which rises with increased slip andthen continues more or less horizontally. While it is a satisfactorytype of curve as to shape, it is amenable to improvement by use of knowncopper facing on the inside of the drum, with the result such as shownby the curve C on FIG. 3, formed by short and long dashes. This hasincreased the torque transmitted at lower slip speeds but has decreasedthem at higher slip speeds, as indicated. The reason for this is thatcopper, being nonmagnetic, in effect increased the magnetic gap with theconcomitant requirement of a higher magnetomotive force required todrive the magnetic field across the gap. At higher slip speeds, thishigher magnetomotive force was rapidly offset with the drooping resultsshown by the right end of curve C. Copper, although resistant tocorrosion (as compared to iron), is soft and therefore not as effectiveas iron to inhibit abrasion by any foreign particles that might be inthe coolant.

Difiiculties were sometimes encountered in plating copper directly toiron or steel, and it was former practice to underlay the copper facingwith a nickel flashing or the like to form a better bond between thecopper and the iron. This resulted in a torque vs. slip-speed curve suchas shown by curve K, which fairly closely follows the curve C. Thus thiscopper-nickel arrangement does not significantly change the droopingcharacteristics of the torque curve. This is apparently for the reasonthat it does not reduce the effects of the nonmagnetic inner face ofcopper in increasing the magnetic gap.

I have discovered that if nickel is employed as the facing A, greatimprovement is effected in the torque vs. slipspeed curve as shown bycurve N on FIG. 3. This closely follows the improved features of curvesC and K in the lower slip range but does not fall off in the higher sliprange. Thus curve N is substantially horizontal over a wide range ofslip speeds in which the curves C and K droop. It is also higher thancurve B throughout the entire slip range.

The use of nickel for the inner facing of the inductor drum 25 is shownat A. I have found that an appropriate range of thickness of the facingA is approximately .005 inch through .030 inch. The thickness employedon a machine such as shown in FIG. 1 and which supplied the data forFIG. 3 was .010 inch for the nickel.

Reasons for the improvement are apparently as follows, although I do notwish to be bound by any theory of operation, the improved results beingindependent of the same. Nickel is magnetic. Therefore, its use as afacing on the inductor drum does not increase the magnetic gap beyondthat of the so-called air gap between the ends of the teeth 23 and theinner face of the drum 25. The meaning of the term air gap is a gapsufficient to permit free running and may be in fact filled with aliquid coolant. The use of any nonmagnetic material at A has thedeleterious effect of increasing the magnetic gap beyond that of the airgap. The magnetic gap is measured by the distance across which the fluxfield must extend without encountering magnetizable material. Thus (FIG.2) if the facing A were nonmagnetic, the magnetic gap would be asindicated at 47. This is greater than the air gap indicated at 49. Withthe facing A composed of nickel, the magnetic and air gaps are the same,namely, as shown at 49.

In view of the above, it is apparent that the magnetic nickel facingreduces (relative to the use of nonmagnetic facing material) themagnetomotive force required to drive a given field from the poles 23into the inductor 25. Therefore, according to curve N the torquetransmission is greater than for curve B at all slip speeds. Moreover,curve N is level at high slip speeds. The reason for this (at leastpartly) is that nickel has electrical resistance which is lower thanthat of the iron of drum 25, although higher than that of any copperfacing that might be used, as heretofore. Thus the eddy currents induceflow in lower resistance paths in the facing A than in iron and thusmore eddy currents are available at higher slip speeds to producetorque. It is to be noted in this connection that most of the eddycurrents in an inductor fiow quite close to the surface being swept bythe concentrated magnetic fields. Thus the fact that the resistance ofthe nickel is lower than that of the iron is quite important to preventdroop of the curve N. I may be questioned why copper would not be betterin this regard because it is a better conductor; but the difliculty withcopper is that it is not magnetic and its effect of increasing themagnetic gap offsets whatever gains are obtained by its use as a lowerresistance eddycurrent conductor on the inductor drum.

It will thus be seen that an important feature of the invention is theuse of a facing such as A, all or a large por tion of which is magneticrather than nonmagnetic. Nickel is such a material and it is of courseto be understood that any other material having similar properties couldbe used. I have found that some tolerances in the resistance range forthe facing A may be had, provided it is lower than that of iron, eventhough it may be higher than that of copper. The following table showsfor two different temperatures comparative figures for resistances ofiron, copper and nickel, these being measured in micro ohm centimeters.Although the metals upon which the table is based are pure, it will beunderstood that in actual practice inclusions of impurities or alloyingmaterials would result in somewhat different resistances. Thus steelmight have a somewhat higher resistance than pure iron. It will also beunderstood that the resistances of copper and nickel might also varysomewhat in practice, depending upon the amount of impurities or thoseadditions therein. It is contemplated, however, that the relativeresistances would be related as shown.

I have determined that a range of resistances desirable for the facing Awould be on the order of from 5 to 8 micro ohm centimeters at 20 C. Withthe preferred nickel facing, the specific resistance is about 6.8 microohm centimeters. It Will be recalled that the desired thickness of thefacing material is in the range of approximately .005 inch to .030 inchwith .010 inch preferred.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. Eddy-current apparatus comprising relatively movable ferromagneticinductor and peripherally polarized field pole members having a runninggap therebetween, means for producing a magnetic field extending throughsaid members and across said gap, a facing on said inductor memberforming one side of said gap, said facing consisting of nickel toestablish a magnetic gap equal to that of the running gap.

2. Eddy-current apparatus comprising relatively rotary ferromagneticinductor drum and peripherally polarized field pole members having arunning gap therebetween, a field coil positioned to produce a magneticfield extending through said members and across said gap, a facing onsaid inductor drum member forming one side of said gap, said facingconsisting of a iayer of a magnetizable metal which has an electricalresistance in the range of approximately 5 to 8 micro ohm centimeters at20 C. and the thickness of which is in the range of approximately .()05to .030 inch.

3. Eddy-current apparatus comprising relatively rotary ferromagneticinductor drum and peripherally polarized 5 6 field pole members having arunning gap therebetween References Cited in the range of approximatelyto /8 inch, 21 field coil UNITED STATES PATENTS positioned to produce amagnetic field extending through 2,447,130 8/1948 Matulaivtis et a1 saidmembers and across said gap, a facing on said 2,971,105 2/1961 Jaeschke310 105 inductor drum member forming one side of said gap, said 5 3,22391 12 19 5 Sh f k et 1 31() 168 facing consisting of a single layer ofnickel the thickness of which is in the range of approximately .005 to.030 ROBERT SCHAEFER: P r Exammerinch. H. O. JONES, Assistant Examiner.

